1. Field of the Invention
The present invention relates to an optical disk provided with read-exclusive and write-enable regions.
2. Description of the Related Art
Optical disks are media on which information can be recorded and from which information can be reproduced by a laser beam or a magnetic field. They can be grouped into three types: reproduction-exclusive or read-exclusive or read-only; information-adding or write-once-read-means; and re-write, depending upon how they are used.
The reproduction-exclusive type optical disk is a transparent disk-like substrate made of glass or resin such as polycarbonate and covered with a reflective film made of a metal such as aluminum. Information is recorded on this film in the form of concaves and convexes, and it is used exclusively for reading.
In the information-adding type, the recording film made of an easily-sublimed material such as tellurium (Te) is formed on the above described substrate and information is recorded on it in the form of holes by laser beam. Information is read by detecting these holes and a writing can be made on it only once.
The re-write type is well known as the one intended to use a magneto-optic effect (MO), phase change or the like. In the one intended to use magneto-optic effect (MO), a vertically magnetized film is formed on the substrate and information is recorded on it in such a way that the magnetic film is magnetized in various directions by heat produced by a strong laser beam and also by a magnetic field produced by additional coils. On the other hand, reproduction of information is carried out by radiating a weak laser beam onto the magnetic film so that the external magnetic field is eliminated, and by detecting polarization plane angles of light thus reflected.
This is intended to use the so-called Kerr effect, according to which polarization plane angles of reflected light differ from one another depending upon the directions of magnetization at a domain, or the Faraday effect, according to which the polarization plane of light rotates when it passes through an opto-magnetic material. For the phase-change type optical disk, the recording film creates two phase changes between non-crystal (or amorphous) and crystal or between two crystal states, depending upon temperature change. Reproduction of recorded signals is carried out using the fact that the reflection factor of light differs depending upon whether the recording film is crystal or non-crystal, or whether the recording film is in a first crystal state or in a second crystal state.
The reproduction-exclusive type optical disk has the advantage that a great many copies can be produced from it. It is used in digital audio and video disks.
The information -adding type optical disk is write-enabled, has a long life and when one writing is made on it, there is little fear of recorded signals being mistakenly erased. It is therefore used, in preference to document files and magnetic tapes, as memory means, image data files and back-ups for re-write type optical disks.
The re-write type optical disk is write-enabled, enables repeated re-writes and is therefore used in external memory means for computing machines.
In the above-mentioned conventional optical disks, however, the entire recording-enable region on the substrate or on the recording film of the substrate is used exclusively as a read or write-enable memory and optical disks having both read- and write-enable regions on the same surface of the substrate are not yet on the market.
The read-only or reproduction-exclusive type optical disk, for example, enables a large quantity of memory to be recorded on it. Further, it can be randomly accessed easily and a great many copies can be produced from it. Furthermore, it is inexpensive and it is therefore assumed that it can be used for word processor dictionaries and font-pattern storage, or disks for program and operation manual storage for computers.
Read-only or reproduction exclusive type optical disks, however, are used exclusively for reproduction and are produced in an exclusive factory. When they are supplied for word processor dictionaries, therefore, users cannot enrich them because they cannot register special font patterns such as "kanji" (Chinese characters) as external characters and special words and phrases necessary for business, cannot be added to the dictionaries.
Some functions are often added to the program and the program is often patched to correct bugs in it. This patching is often made to a short program.
When a program stored in a reproduction-exclusive type optical disk is supplied to users, therefore, they cannot re-write the program data. Even when the program can be corrected by patching, they are forced to buy a new reproduction-exclusive type optical disk to make a minor correction to the program.
Further, it is a big burden to program suppliers and it is unrealistic to produce new reproduction-exclusive type optical disks every time programs are corrected.
It is therefore supposed that demand for an optical disk with a write-enable region on which users can write any information they like, as well as a read-exclusive region, will increase in the future.
An optical disk having read-exclusive and write-enable regions will be used so that items such as mathematical formulae which do not need to be rewritten are recorded on its read-exclusive region and that operational and process results are recorded on its write-enable region.
Two kinds of mark-length and mark-position recording systems are well known for these information recording systems.
FIG. 1 is intended to explain the mark length recording system. In this recording system, an edge 3 and 4 of a recording pit 2 denotes signal "1" and an unedged portion represents signal "0." Signals 6 are recorded on the disk in response to clocks 5 which are synchro signals for recording information.
More specifically, an edge 3 of the recording pit 2 on which the scanning laser beam passes when it passes from the disk surface 1 onto the recording pit 2 or edge 4 of the recording pit 2 onto which the scanning laser beam passes when it comes out of the recording pit 2 onto the disk surface 1 represents signal "1", while the surface 1 of the disk which does not have an edge 4 or flat plane of the recording pit 2 denotes signal "0". Information is reproduced by detecting whether or not edge 3 or 4 of the recording pit 2 is present in the positions corresponding to clocks 5, radiated by a reading laser beam. This mark length recording system is also called the recording system intended to use mark length modulation.
FIG. 2 is intended to explain the mark position recording system. Signal "1", corresponding to a clock 15, is recorded on the disk, when recording pit 12 is formed there by the laser beam irradiation, and signal "0" is recorded when no recording pit 12 is formed on the disk. For this mark position recording system, information is read by detecting whether or not the recording pit 12 is present at the position corresponding to clock signal 15. This mark position recording system is also called the recording system intended to use mark position modulation.
In comparing the above two recording systems it is found that the mark length recording system has a recording density two times that of the mark position recording system. This is because it is intended o record information on the disk using edges 3 and 4 of a hole (or recording pit 2). For the mark length recording system, however, position control for accurately detecting edges 3 and 4 of the recording pit 2 becomes more complicated because edges 3 and 4 of the recording pit 2 must be detected in synchronization with clock signals 5. Therefore, the mark length recording system has been applied to the optical disk of the read-exclusive type and the mark position recording system has been applied to the optical disk of the write-enable type.
More specifically, the mark length recording system is employed for the read-exclusive type optical disk because concave and convexe portions can be pre-formed on the disk with high positional accuracy. The rotation control of the optical disk is carried out according to a CLV (constant linear velocity) method. On the other hand, the mark position recording system is employed for the write-enable type optical disk because it is difficult to accurately position the recording pits on the disk. The rotation of the disk is controlled in this case according to the CAV (constant angular velocity) method.
In the CLV method, the linear velocity at which information is recorded on a track of a disk and reproduced from it is made constant for all tracks. As the tracks approach the outer circumference of the disk, therefore, the number of recording pits formed per track becomes larger. This enables a higher memory capacity. However, the rotation control of a spindle motor for driving the optical disk becomes more complicated.
In the CAV method, the rotational velocity of the spindle motor is constant and the recording and reproducing frequency is not changed. This simplifies control of the spindle motor and the control circuit system for the spindle motor and enables the spindle motor itself to be made smaller. However, the memory capacity per track on the disk is determined by the number of marks (or information content) which can be recorded on the innermost track of the disk. The total memory capacity of the disk is thus made smaller than that with the CLV method.